"We don't have an answer for that question yet," says Mark A. Pereira, an epidemiologist at Children's Hospital in Boston and Harvard Medical School and the lead author of the study, published in April in the Journal of the American Medical Association.

The study's authors looked at the association between dairy foods and insulin resistance syndrome - a bundle of symptoms that includes obesity, high blood pressure, abnormal blood fat levels, high levels of blood glucose and insulin resistance. In insulin resistance, the body's tissues become less sensitive to the action of insulin, which normally helps cells use blood sugar as a fuel.

The elements of insulin resistance syndrome are risk factors for diabetes and heart disease. Pereira's group attempted to examine the role that dairy products play in the development of the syndrome. They observed that dairy consumption has dropped in recent decades - as obesity and diabetes have risen.

The researchers used data obtained in a study of heart disease risk factors among 3,157 young adults, ages 18 to 30, in four cities. The subjects received clinical exams and questionnaires for demographic and behavioral information, such as smoking and exercise, and participated in detailed interviews - at seven-year intervals - about their diets.

Among individuals who were overweight when they joined the study, dairy consumption was related to a lower risk of insulin resistance syndrome. Among those who reported eating five or more servings of dairy products a day, the adjusted odds of developing the syndrome were 72 percent lower than among those who ate an average of less than 10 servings a week. The link was similar for blacks and whites and for men and women.

But is it milk, or a pattern of eating? Researchers note that the dairy consumers also tended to eat more whole grain, fruit, vegetables and saturated fat, but less sugar-laden soft drinks.

"Soda may be one of the important factors here," says Pereira, who noted that federal surveys suggest that children increasingly are replacing milk with soda.

Also, he says, milk may be more satisfying than other choices, so that people who hit the dairy case are less likely to overeat during the day. A version of this story first ran on April 24.